import React, { Component } from "react";

export default class Count extends Component {
    state = { count: 0 };

    /**
     * 加法
     */
    increment = () => {
        const { value } = this.selectedNumber;
        const { count } = this.state;
        this.setState({ count: count + value * 1 });
    };

    /**
     * 减法
     */
    decrement = () => {
        const { value } = this.selectedNumber;
        const { count } = this.state;
        this.setState({ count: count - value * 1 });
    };

    /**
     * 奇数加
     */
    incrementIfOdd = () => {
        const { value } = this.selectedNumber;
        const { count } = this.state;
        this.setState({ count: count % 2 !== 0 ? count + value * 1 : count });
    };

    /**
     * 异步加
     */
    incrementAsync = () => {
        const { value } = this.selectedNumber;
        const { count } = this.state;
        setTimeout(() => {
            this.setState({ count: count + value * 1 });
        }, 500);
    };

    render() {
        return (
            <div>
                <h1>当前求和为：{this.state.count}</h1>
                <select ref={(c) => (this.selectedNumber = c)}>
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                </select>
                &nbsp;
                <button onClick={this.increment}>+</button>&nbsp;
                <button onClick={this.decrement}>-</button>&nbsp;
                <button onClick={this.incrementIfOdd}>
                    当前求和为奇数再加
                </button>
                &nbsp;
                <button onClick={this.incrementAsync}>异步加</button>&nbsp;
            </div>
        );
    }
}
